.On Aquatic Carnimrous Coleoptera or Dytiscidce. 895 



less conspicuous, setjB ; the liind coxre are large, and the wings of the raetasternum 

 are deflexed outside them as slender nearly parallel-sided bands. The hind legs are 

 rather slender, but their femora have a rectangular apical angle ; their tarsi have 

 no lobing of the joints externally and are terminated by two short, stout, very 

 nearly equal claws. The male characters are highly peculiar ; the front tarsi are 

 not broad, but are incrassate and compressed, and bear beneath some pencils of 

 long setae, mixed with which are three or four transverse series of small palettes, 

 and they bear extremely long claws ; the last ventral segment is marked by two 

 very deep parallel liaes running along its middle. 



This interesting and very rare North American insect, has no close allies, the 

 peculiar coxal lines and processes, are not very different to what exist in iMatus, 

 but it is worthy of remark that it is the Australian, not the North American, 

 species of Matus that most approach it. The male tarsi are an approximation to 

 what exists in some Colymbetini, the peculiar Dytiscus pustulatus (No. 945), for 

 example. 



I. 58.— Genus MATUS. {Vide^. 599.) 



Three species form this aggregate ; their individuals are of rather narrow parallel 

 form, but a good deal attenuate behind, and with very broad head. The prosternum 

 is sulcate along the middle, the groove extending from near the front margin of 

 the prosternum to the apex of the prosternal process : the side of the prothorax 

 has a raised margin. 



The middle coxse are rather widely separated, and the intercoxal process of the 

 metasternum bears in front a highly developed cavity for the apex of the prosternal 

 process. The hind coxie are very large, and their front border approaches very 

 close to the middle coxa, the wings of the metasternum are therefore very short, 

 and greatly deflexed as slender bands outside the front part of the hind coxte, this 

 band is in its terminal portion so excessively slender that it is truly an acuminate 

 line ; the coxal lines are deep, and start in front from the apex of the metasternum 

 and are parallel or subparallel till they approach the coxal lobes, and then are 

 gently turned outwards, leaving a broad supra-articular border. The hind legs are 

 well developed for swimming, being rather short and stout, and their tarsi are 

 peculiar, the hind margins of the joints being well lobed externally ; but the lobe, 

 or produced part, is here at the upper edge, whereas in the other genera where a 

 lobinof of this sort occurs it is at the lower edgfe of the tarsus ; the two claws 

 terminating the tarsus are straight, and slender, and very unequal in length, the 

 outer one being about twice as long as the inner one. 



The surface is polished and almost without sculpture ; the male tarsi are but 

 little developed. 



The genus is again an isolated one ; the species when seen from above suggest 



